The control of cellular differentiation in Volvox is under the influence of a species specific sex hormone secreted by the sperm. This hormone initiates the syntheses leading to the formation of a sexual embryo (male in the male strain, female in the female strain) but such syntheses are controlled by various genetic loci. Research has been initiated on the hormone produced by monoecious species; this is of interest since, unlike in dioecious species, such hormones are not species-specific. A mutant in the male strain of V. carteri f. weismannia is also being investigated; this mutant shows only the asexual morphological form with the sperm packets being formed from large "gonidia-like cells. Further isolation of new strains will be continued using soil samples from all over the world.